I think it is summed up by the Borg themselves when they refer to resistance as "futile" or "irrelevant".  They do not think they will lose or allow room for negotiation.  The attack on the USS Cole was by a much smaller craft but it was the thought that they were doing what they thought was the way and it WILL succeed.  This stems from the understanding that there are many more (from the hive) to take up the fight without question.  This has a serious effect on the psyche of the adversary.
The efficiency question is from The Borg ignoring craft that they do not see as a threat or having desired traits or technology.  This and there being two typed of drones, assimilated and born, she will have her roles more specialized than terrestrial insect queens.  Taking the cortex in humans and adding the neocortex for something more than fight or flight then it is not too much to extrapolate a behavior pattern for the Borg governing a massive multi species area of space with radically different tech levels from one to Q.  The Queen understands that sometimes a whisper has more effect than a shout and may potentially save Her race from onslaught.